Luminance signal/color signal separator circuit

Abstract: A luminance signal/color signal separator circuit having an input terminal (11) and luminance and color output terminals (18),(17) includes a comb filter (13) connected between the input terminal (11) and the color output terminal (17); an amplitude detector (16) having an input connected to the color output terminal; a filter (12),(15) having a first input connected to the input terminal (11) and a second input connected to an output of the amplitude detector (16); and a combiner (14) having an output connected to the luminance output terminal (18), a first input connected to the input terminal (11) and a second input connected to an output of the filter (12),(15). The separator circuit processes a composite signal which includes an original luminance signal and an original color signal. The filter (12),(15) passes a gain controlled color band signal. A signal at the luminance output terminal (18) includes a signal component characterized by an amplitude in a color band frequency range, and the combiner (14) outputs the signal having a signal component amplitude as (1) a first amplitude when the original color amplitude is small, and (2) a second amplitude when the original color amplitude is large, the first amplitude being greater than the second amplitude.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns luminance signal/color signal separator circuits used in devices which process the picture signals of color television receivers, video tape recorders, etc. 2. Description of Related Art In devices which process the picture signals of color television receivers, video tape recorders (hereafter, VTR), etc., a complex composite signal, in which the luminance signal (hereafter, Y signal) and the color signal (hereafter, C signal) were previously mixed to form the complex composite signal, is used as the video signal. The Y signal and the C signal have to be separated from this type of video signal. This separation is called Y/C separation. Figure 3 is a graph of the frequency spectrum of this type of video signal. The vertical axis expresses amplitude, and the horizontal axis expresses frequency. In Figure 3, the Y signal in the video signal has a frequency spectrum or range of from 0 to about 4.5 MHz. The C signal also has a specified band, referred to herein as the C-band, about a color secondary carrier wave frequency of 3.58 MHz (the secondary carrier wave is a substantially pure narrow band signal within the C-band of the spectrum). The Y signal and the C signal have an interleaved relationship, and they are to be separated, spectrum-wise, for example, 1.5 MHz at the low band side of 3.58 MHz and 0.5 MHz at the high band side. Figure 4 is a block diagram showing a simple luminance signal/color signal separator circuit which separates the Y signal and the C signal from this type of video signal. In Figure 4, 41 is an input terminal to which video signal a2 is supplied. Video signal a2 is supplied to band-pass filter (hereafter, BPF) 42 and low-pass filter (hereafter LPF) 43. BPF 42 passes the C-band component of video signal a2 including the color secondary carrier wave and all other signals in the C-band frequencies which are present on video signal a2. By this means, BPF 42 extracts and supplies C signal b2 to C signal output terminal 44. LPF 43 passes a low band component of video signal a2 having frequencies lower than the frequencies of the C-band component on video signal a2. By this means, LPF 43 extracts and supplies Y signal c2 to Y signal output terminal 45. Figure 5 is a graph showing the C signal b2 output from BPF 42. The vertical axis expresses amplitude, and the horizontal axis expresses frequency. As shown, C signal b2 output from BPF 42 covers the C-band component of video signal a2. Figure 6 is a graph showing the Y signal c2 output from LPF 43. The vertical axis expresses amplitude, and the horizontal axis expresses frequency. As shown, Y signal c2 output from LPF 43 covers a low band component of video signal a2 having frequencies lower than frequencies of the C-band component. When using this type of luminance signal/color signal separator circuit, all frequency components in the original video signal in the frequency range about the C-band component is eliminated from Y signal c2 output from Y signal output terminal 45, and a broad-band luminance signal cannot be obtained. Therefore, Y signal c2 has a narrower spectrum than the original Y signal, and therefore, the horizontal resolution of a display of Y signal c2 is lower compared to a display of the original Y signal when the picture is displayed on a screen. Also, C signal b2 contains those components of the original Y signal having frequency components falling in the C-band about the color secondary carrier wave frequency, those components, constituting noise, remaining as a residual Y signal in C signal b2 output from C signal output terminal 44. This residual Y signal interferes with subsequent signal processing. Figure 7 is a block diagram showing a luminance signal/color signal separator circuit which uses a C signal comb filter circuit. In Figure 7, 51 is an input terminal to which video signal a3 is supplied. Video signal a3 is supplied to BPF 52 and, at the same time, to a first input terminal of subtractor 53. BPF 52 passes the C-band component of video signal a3 including the color secondary wave and all signals in the C-band frequencies which are present on video signal a3. By this means, BPF 52 extracts and supplies C signal b3 to C signal comb filter circuit 54. Comb filter circuit 54 eliminates the residual Y signal from C signal b3 by using Y signal line correlation. Then comb filter circuit 54 supplies purified C signal c3 to a second input terminal of subtractor 53 and, at the same time, to C signal output terminal 55. Subtractor 53 produces purified Y signal d3 by subtracting purified C signal c3 from video signal a3, and supplies purified Y signal d3 to Y signal output terminal 56. Figure 8 is a block diagram showing C signal comb filter circuit 54 in Figure 7. In Figure 8, 61 is an input terminal to which C signal b3 is supplied from BPF 52. C signal b3 is supplied to "one horizontal scanning cycle" delay circuit (hereafter, 1H delay circuit) 62 and, at the same time, to a first input terminal of subtractor 63. 1H delay circuit 62 delays C signal b3 from input terminal 61 by a 1H delay and supplies this delayed signal to gain control circuit 64 as 1H delay color signal e3. Gain control circuit 64 controls the amplitude of 1H delay color signal e3 and supplies this to a second input terminal of subtractor 63 as gain controlled 1H delay color signal f3. Subtractor 63 produces purified C signal c3 by subtracting gain controlled 1H delay color signal f3 from C signal b3, and supplies this to output terminal 66. Figure 9 is a graph showing the gain property of C signal comb filter circuit 54. The vertical axis expresses gain, and the horizontal axis expresses frequency. As shown in Figure 9, the gain of C signal comb filter circuit 54 takes a comb-shape in frequency. Figure 10 is an enlargement along the horizontal axis of portion A in Figure 9. As shown in Figure 10, when the frequency of the C signal is an integral multiple of the 1H frequency (i.e., fH = 1/1H), the amplitude property of C signal comb filter circuit 54 takes a minimum value. When the frequency of the C signal is a frequency based on fH/2 being added to an integral multiple of the 1H frequency (i.e., fH = 1/1H), the amplitude property takes a maximum value. Thus, a frequency component in a signal input to C signal comb filter circuit 54 having a frequency equal to an integral multiple of the 1H frequency (i.e., fH = 1/1H), is attenuated. However, a frequency component of a signal having a frequency equal to fH/2 added to an integral multiple of the 1H frequency (i.e., fH = 1/1H) passes through C signal comb filter circuit 54 with hardly any attenuation. For this reason, video signal a3, supplied to input terminal 51 in Figure 7, is also supplied to the second input terminal of subtractor 53 as purified C signal c3 from which the residual Y signal has been eliminated by passing through BPF 52 and C signal comb filter circuit 54. Figure 11 is a graph showing purified C signal c3. The vertical axis expresses amplitude, and the horizontal axis expresses frequency. Purified C signal c3, output from C signal comb filter circuit 54, has a comb type property in which the residual Y signal has been eliminated from the C-band frequencies of signals passing through BPF 52. Subtractor 53 produces purified Y signal d3 by subtracting purified C signal c3 from video signal a3, and supplies purified Y signal d3 to Y signal output terminal 56. Figure 12 is a graph showing purified Y signal d3. The vertical axis expresses amplitude and the horizontal axis expresses frequency. Purified Y signal d3, output from subtractor 53, from which the original C signal component (at the color secondary wave frequency) in the C-band frequencies has been eliminated, is in an interleaved relationship with purified C signal c3 shown in Figure 11. By this means, the luminance signal/color signal separator circuit of Figure 7 leaves the residual Y signal component within the C-band frequencies in purified Y signal d3. Thus, the band can be sufficiently purified. When using this type of luminance signal/color signal separator circuit, the Y signal can be sufficiently purified. At the same time, the residual Y signal can be removed from the C signal. However, this construction obtains the Y signal by subtracting the C signal, which has passed through the series connection of a band-pass filter and a C signal comb filter circuit, from a video signal. The BPF is a high-order filter and its gain randomness and phase randomness are large. Thus, it is necessary to accurately control both the gain and phase together with the gain randomness of the C signal comb filter circuit. For this reason, it is difficult to minimize the manufacturing cost of equipment which includes such a luminance signal/color signal separator circuit. In the above described luminance signal/color signal separator circuit, the band of the luminance signal can be sufficiently purified. At the same time, the residual luminance signal can be eliminated from the C signal. However, the BPF required is a high-order filter, and its gain randomness and phase randomness are large. Thus, it is necessary to accurately control both the gain and the phase together with the gain randomness of the C signal comb filter circuit. As a result, it is difficult to minimize the manufacturing cost of equipment which include this type of luminance signal/color signal separator circuit. It is an object of the present invention to eliminate the above problem. It is another object to provide a luminance signal/color signal separator circuit which obtains a broad-band luminance signal without the series connection of a band-pass filter and a C signal comb filter circuit and, at the same time, is capable of eliminating any residual luminance signal from the C signal. In Japanese laid open patent JP-A-417485 the Y signal is separated from the composite signal by adding a composite signal to a 1H delayed composite signal (since the phase of the C signal is inverted every 1H delay) and the C component remaining mixed in the Y signal is removed by eliminating a specific band of frequencies about 3.58 MHz when the separated C signal has a high saturation level. However, the 4-17485 Japanese laid open patent does not use a band pass filter or disclose the Y signal being extracted by combining a composite signal with a specified C band component of the composite signal. US-A-4232330 is considered to be the closest prior art to the present invention and discloses a separator to process a composite input signal into a first signal based on a second output signal, the composite input signal being a combination of a first input signal having a first frequency range and a second input signal having a second frequency range overlapping with the first frequency range, in which the separator generates a detection signal corresponding to an amplitude of the second output signal. Patent Abstracts of Japan Vol. 16, no. 352 and JP-A-4108286 discloses a luminance/colour signal separating circuit having a filter to separate the colour signal from the combined luminance/colour signal and a controllable gain amplifier and a level detector connected to the output of the filter, whereupon the colour signal output of the controllable amplifier is subtracted from the input signal to obtain the luminance signal. According to a first aspect of the present invention, there is provided a separator circuit to separate a luminance output signal from a composite input luminance/colour signal comprising first circuitry to generate a colour output signal and a detection signal corresponding to the amplitude of the colour output signal, characterized in that the separator circuit further comprises: second circuitry to generate a compensation signal from the composite input signal, the compensation signal having a frequency range covering the frequency range of the colour signal and having an amplitude dependent on the detection signal; and third circuitry to generate the luminance output signal from a combination of the compensation signal and the composite input signal. According to a second aspect of the present invention, there is provided a method of separating a luminance output signal from a composite input luminance/colour signal comprising the steps of: filtering the composite input signal to generate a colour output signal; generating a detection signal corresponding to the amplitude of the color output signal characterized in that the method further comprises the steps of: filtering the composite input signal to generate a compensation signal, having a frequency range containing the frequency range of the colour output signal and having an amplitude dependant on the detection signal; and combining the compensation signal and the composite input signal to generate the luminance output signal. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in detail in the following description of preferred embodiments with reference to the following figures wherein: Figure 1 is a block diagram showing an embodiment of the luminance signal/color signal separator circuit of this invention; Figure 2 is a graph showing the Y signal gain property of the luminance signal/color signal separator circuit subtractor in Figure 1; Figure 3 is a graph showing a typical video signal input to a related art luminance signal/color signal separator circuit; Figure 4 is a block diagram illustrating a simple luminance signal/color signal separator circuit; Figure 5 is a graph showing the C signal output from the BPF in Figure 4; Figure 6 is a graph showing the Y signal output from the LPF in Figure 4; Figure 7 is a block diagram showing a related art luminance-signal/color signal separator circuit in which a C signal comb filter circuit is used; Figure 8 is a block diagram showing the C signal comb filter circuit used in the circuit of Figure 7; Figure 9 is a graph showing the gain property of the C signal comb filter circuit in Figure 7; Figure 10 is an enlargement drawing in which portion A of Figure 9 is expanded on the horizontal axis; Figure 11 is a graph showing the C signal from the C signal output terminal in Figure 7; and Figure 12 is a graph showing the Y signal from the Y signal output terminal in Figure 7. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The following is a description of an embodiment of this invention with reference to the drawings. Figure 1 is a block diagram showing an embodiment of the luminance signal/color signal separator circuit of the present invention. In Figure 1, 11 is an input terminal to which video signal a1 is supplied. Video signal a1 is supplied to BPF 12 and C signal comb filter circuit 13 with an additional filter function to roughly remove low band components and, at the same time, it is supplied to a first input terminal of subtractor 14. C signal comb filter circuit 13 produces purified C signal c1 by eliminating the Y signal components from video signal a1 using Y signal line correlation. Then C signal comb filter circuit 13 supplies purified C signal c1 to amplitude detector circuit 16 and, at the same time supplies purified C signal c1 to C signal output terminal 17. Amplitude detector circuit 16 detects the amplitude of purified C signal c1 from C signal comb filter circuit 13, and supplies detection signal d1, which expresses this detection result, to amplitude limiter circuit 15. BPF 12 extracts C-band signal b1 by passing the C-band component of video signal a1 including the color secondary carrier wave and all other signals in the C-band frequencies which are present on video signal a1, and supplies this C-band component to amplitude limiter circuit 15. Amplitude limiter circuit 15 controls the gain applied to C-band signal b1 so as to produce gain controlled C-band signal e1 based on detection signal d1 by limiting the amplitude of C-band signal b1. The output of amplitude limiter circuit 15 is supplied to a second input terminal of subtractor 14 as gain controlled C-band signal e1. Subtractor 14 produces purified Y signal f1 by subtracting gain controlled C-band signal e1 from video signal a1, and supplies this to Y signal output terminal 18. The following is a description of the operation of this embodiment. Video signal a1, input to input terminal 11, is processed to become purified C signal c1 from which the Y signal component is eliminated by passing through C signal comb filter circuit 13, and is output from C signal output terminal 17. By this means, purified C signal c1 is obtained from video signal a1. Amplitude detector circuit 16 detects the amplitude of purified C signal c1 and supplies detection signal d1, which expresses this detection result, to amplitude limiter circuit 15. The C-band signal b1 is extracted from video signal a1 by passing through BPF 12. The C-band signal b1 in this case includes the color secondary carrier wave and other signals in the C-band frequencies which are present in video signal a1. When the amplitude of the original C signal in video signal a1 is large, amplitude detector circuit 16 detects that the amplitude of purified C signal c1 is large, and detection signal d1 controls amplitude limiter circuit 15 to limit the amplitude of C-band signal b1 by controlling gain (e.g., attenuating) applied to C-band signal b1 so as to produce a large amplitude gain controlled C-band signal e1. By this means, purified Y signal f1 from subtractor 14 is a Y signal in which both the C-band component of the original Y signal and the original C signal are greatly reduced. When the amplitude of the original C signal in video signal a1 is small, amplitude detector 16 detects that the amplitude of purified C signal c1 is small. Then detection signal d1 controls amplitude limiter circuit 15 to limit the amplitude of the C-band signal b1 by controlling the gain (e.g., attenuating) applied to C-band signal b1 so as to produce a small amplitude gain controlled C-band signal e1. Thus, only a small amplitude signal for the gain controlled C-band signal e1 is required. Since the amplitude of the gain controlled C-band signal e1 is small, the original C signal in video signal a1 will be attenuated in purified Y signal f1 from subtractor 14 while the original Y signal in video signal a1 is not substantially attenuated. Figure 2 is a graph showing the gain property of the luminance signal/color signal separator circuit with respect to the output of purified Y signal f1 from subtractor 14. The vertical axis expresses gain, and the horizontal axis expresses frequency. As shown at f1A in Figure 2, when the amplitude of the original C signal in video signal al is large, both the C-band component of the original Y signal and the original C signal are greatly reduced in purified Y signal f1 by subtractor 14. Therefore, signals over the entire C-band centered on the color secondary carrier wave frequency (3.58 MHz) is greatly attenuated. As shown at f1B in Figure 2, when the amplitude of the original C signal in video signal al is small and the amplitude of the C-band component of the original Y signal in video signal al is large, the original C signal is reduced from purified Y signal f1; however, the C-band component of the original Y signal is not greatly reduced, and other signals, except the color secondary carrier wave, in the C-band centered on 3.58 MHz are not greatly attenuated. When using this embodiment, purified C signal c1 from which the C-band component of the original Y signal has been sufficiently eliminated is obtained from C signal output terminal 17. At the same time, when the amplitude of the original C signal is small in video signal a1, purified Y signal f1, in which the C-band component of the original Y signal is little attenuated, is obtained from Y signal output terminal 18. By this means, a picture with little color reproduction distortion and color noise is obtained. At the same time, when the amplitude of the original C signal is small in video signal a1, satisfactory horizontal resolution is obtained. Also, since the BPF and the C signal comb filter circuit are not connected in series, control of gain and phase for both circuits together is not required. Moreover, a second-order filter may be used for the BPF, and thus there is little gain randomness or phase randomness. For this reason, the BPF and the C signal comb filter circuit can be used without controls. By this means, the manufacturing cost of equipment which include the disclosed luminance signal/color signal separator circuit can be reduced. In the embodiment in Figure 1, BPF 12 is used as the means for passing the C-band components of video signal a1 including the color secondary carrier wave and other signals in the C-band frequencies of video signal a1. However, if some degree of gain and phase control is exercised, a high pass filter may be used. When using this invention, a broad-band luminance signal can be obtained without connecting the band-pass filter and the color signal comb filter circuit in series. Therefore, control of the gain and phase for both together is not required. Moreover, a second-order filter may be used for the band-pass filter, and thus there is little gain randomness or phase randomness. For at least this reason the band-pass filter and the color signal comb filter circuit can be used without controls. By this means, the manufacturing cost of equipment which include this luminance signal/color signal separator circuit can be reduced. Furthermore, high resolution signals can be obtained when separating a video signal in which the color signal level is small. Having described preferred embodiments of a novel luminance signal/color signal separator circuit, and a method for separating signals, which are intended to be illustrated and not limiting, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. For example, other filter circuits may be substituted for BPF 12. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope of the invention as defined by the appended claims.

Claims: A separator circuit to separate a luminance output signal from a composite input luminance/colour signal comprising first circuitry (13, 16) to generate a colour output signal and a detection signal corresponding to the amplitude of the colour output signal, characterized in that the separator circuit further comprises: second circuitry (12, 15) to generate a compensation signal from the composite input signal, the compensation signal having a frequency range covering the frequency range of the colour signal and having an amplitude dependent on the detection signal; and third circuitry (14) to generate the luminance output signal from a combination of the compensation signal and the composite input signal. A separator circuit as claimed in claim 1, wherein: the colour signal component of the composite input signal has a first signal amplitude; the output luminance signal includes a signal component having a frequency range contained within the frequency range of the colour output signal; and the third circuitry (14) generates the output luminance signal in the frequency range contained within the frequency range of the colour signal component of the composite input signal having an amplitude which is greater when the amplitude of the colour signal component of the composite input luminance/colour signal is small than when the amplitude of the colour signal component of the composite input luminance/colour signal is large. A separator circuit as claimed in claim 1 or 2, characterized in that the first circuitry (13, 16) includes means (13) for generating as the colour output signal the colour signal component of the composite input signal. A separator circuit as claimed in claim 3, characterized in that the means (13) for generating the colour output signal includes a comb filter. A separator circuit as claimed in any preceding claim, characterized in that the third circuitry (14) includes combining circuitry to generate the luminance output signal by subtracting the compensation signal from the composite input signal. A separator circuit as claimed in any preceding claim, characterized in that the first circuitry (13, 16) also includes an amplitude detector (16) to generate the detection signal. A separator circuit as claimed in any preceding claim, characterized in that the second circuitry (12, 15) includes: a filter (12) to generate an intermediate signal from the composite input signal, the intermediate signal having a frequency range covering the frequency range of the colour output signal; and an amplitude scaling circuit (15) to generate the compensation signal from the intermediate signal, by controlling an amplitude of the compensation signal based on a function of the detection signal. A separator circuit as claimed in claim 7, characterized in that the amplitude scaling circuit (15) includes a scalable attenuator, the scalable attenuator attenuating the intermediate signal by an attenuation proportional to the amplitude of the detection signal to produce the compensation signal. A separator circuit as claimed in claim 1, characterized in that the luminance output signal includes a signal component having a component frequency range which is contained within the frequency range of the colour signal, the separator circuit being arranged such that the gain of the separator circuit in respect of the luminance output signal over the component frequency range is greater when the amplitude of the colour signal component of the input composite signal compared to that of the total input composite signal is low than when the amplitude of the colour signal component of the input composite signal compared to that of the total composite input signal is high. A method of separating a luminance output signal from a composite input luminance/colour signal comprising the steps of: filtering the composite input signal to generate a colour output signal; generating a detection signal corresponding to the amplitude of the colour output signal characterized in that the method further comprises the steps of: filtering the composite input signal to generate a compensation signal, having a frequency range containing the frequency range of the colour output signal and having an amplitude dependant on the detection signal; and combining the compensation signal and the composite input signal to generate the luminance output signal. A method as claimed in claim 10, characterized in that: the luminance output signal includes a signal component having a frequency range contained within the frequency range of the colour signal; the step of combining includes outputting the luminance output signal having an amplitude of the signal component as a first component amplitude when the second signal amplitude is small and a second component amplitude when the second signal amplitude is large, the first component amplitude being greater than the second component amplitude.

Inventors: KAWANO MITSUMO, KUSANO TAKAHIRO, KAWANO, MITSUMO, KUSANO, TAKAHIRO, KAWANO, MITSUMO, INTELLECTUAL PROP. DIVISION, KUSANO, TAKAHIRO, C/O INTELLECTUAL PROP. DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1994
Main classification: H04N9
IPC codes: H04N9